Accessing a communications network

ABSTRACT

A method and node in a communication network for facilitating access by a client terminal to an IMS service from a non-Session Initiation Protocol (non-SIP) compliant access network such as a circuit-switched network. The node receives a request from the client terminal and in response, allocates to the terminal, a Terminal Adapter from a plurality of Terminal Adapters. The node then sends a message to the client terminal reporting the address of the allocated Terminal Adapter.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for accessing acommunications network, and in particular to a method of allocating aTerminal Adapter to allow User Equipment to access an IP MultimediaSubsystem network from a Circuit Switched access network.

BACKGROUND TO THE INVENTION

Unstructured Supplementary Service Data (USSD) is defined in GSM 02.90(UMTS 22.090) and GSM 03.90 (UMTS 23.090). It is a technology built intoGlobal System for Mobile Communications (GSM) standards for supportingthe transmission of information over GSM networks, and can also be usedwith Universal Mobile Telecommunications Systems (UMTS) technologies.USSD allows text-based user interaction between applications based on aGSM/UMTS Public Land Mobile Network (PLMN) and User Equipment (UE). USSDis used as a “trigger” to invoke services or applications.

A USSD message may be initiated by either the network, the UE (the termUE is herein used as a generic name that incorporates Mobile Stations,MS, and other terminal types) or a subscriber using the UE. In networkinitiated USSD messages, the network may either request information fromthe UE, or text strings may be simply sent and displayed to the UE.Referring to FIG. 1, there is illustrated schematically an example of aknown routing of a USSD message, as described in 3GPP TS 23.078 and U.S.Pat. No. 5,752,188.

USSD messages contain a Service Code (SC) that identifies the action tobe taken on receipt of the USSD message. For UE initiated USSD messagesthe SC is generated by the UE or the subscriber and includes digits,letters, and/or signs. Any SC that is not recognised by the UE isinterpreted as USSD by the UE. SCs that are recognized are mapped toSupplementary Service Operations (SS-Operations) defined in GSM/UMTS,for example Registration/Deregistration/Activation/De-activation, andInterrogation of supplementary service such as Call Forwarding or CallBarring.

Unrecognized SCs are transmitted in USSD messages from the UE to aMobile Switching Centre (MSC)/Visitor Location Register (VLR) on thenetwork. The MSC/VLR comprises a USSD handler, which analyses the SC. Ifthe USSD handler recognizes the SC, then the action that the SC triggersis performed. That is to say, if an application that corresponds to theSC resides in the MSC/VLR, the USSD handler delivers the USSD to thisapplication.

If the USSD handler at the MSC/VLR does not recognize the SC, the USSDmessage is forwarded to the subscriber's Home Location register (HLR).The HLR also comprises a USSD handler, which analyses the SC todetermine if there is an HLR internal application that corresponds tothe SC. The USSD is delivered to this application if there is a match.

If the USSD handler at the HLR does not recognize the SC, the HLR checksthe USSD General CAMEL Service Information (UG-CSI) to see if there isan HLR external application that corresponds to the SC. The address tothe external node is found in the UG-CSI. The address to the externalnode may be unique for each subscriber, unique for a group ofsubscribers, or may be the same for all subscribers using that HLR. Theexternal nodes hosting USSD applications may be, for example, a GSMService Control Function (gsmSCF), an information service (for exampletoday's news or weather), or a translator between the USSD format overSS7 and a protocol carried over IP (for example a Web Service/SOAP basedprotocol).

U.S. Pat. No. 6,330,445 describes an optimized routing of USSD, asillustrated in FIG. 2, which allows an MSC/VLR that receives a USSDmessage to directly route the message to PLMN external nodes.

IMS Centralised Services (ICS) is described in 3GPP Release 8, andenables IMS services to be offered accessed using different types ofaccess network, including Circuit Switched (CS) networks. A ServiceEngine resides in the IMS network and the CS network is used only toaccess IMS services. One way to provide access to IMS services from a CSnetwork is to use a Terminal Adapter (TA) that emulates an IMS terminal.The TA communicates with the accessing terminal on one side and the IMSService Engine on the other side. The TA effectively acts as a gatewaybetween a protocol carried over USSD and the SIP/XCAP signaling used inIMS. So, for example, a TA may “translate” USSD messages into a SIPINVITE message to initiate a session with a peer UE. It is possible foran ICS subscriber to roam into any CS PLMN, which may or may not be ICScapable. It is therefore desirable to allow allocation of a TA to asubscriber both in legacy networks that do not have ICS functionalityand in ICS capable networks.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a methodof facilitating access by a client terminal to an IMS service from anon-Session Initiation Protocol compliant access network, the methodcomprising:

-   -   receiving a request message from the client terminal;    -   in response to receipt of said request message, allocating to        the client terminal a Terminal Adapter from a plurality of        Terminal Adapters;    -   sending to the client terminal a message reporting the address        of the allocated Terminal Adapter.

It is preferred that the steps of the method are carried out at a singlenode.

The non-Session Initiation Protocol compliant access network may be aCircuit Switched access network.

In order to assist allocation of a Terminal Adapter, the request messagemay contain an identifier that identifies the User Equipment, the methodcomprising allocating a Terminal Adapter depending upon the identifier.The identifier may be selected from one of an International MobileEquipment Identity, IMEI, and a Medium Access Control, MAC, address.

The plurality of Terminal Adapters may comprise groups of TerminalAdapters, each group relating to a User Terminal type.

The plurality of Terminal Adapters may comprise groups of TerminalAdapters, each group relating to a service type.

The method preferably comprises, prior to allocating a Terminal Adapter,sending a query to a subscriber database and/or a terminal database; and

-   -   receiving a response from the subscriber database and/or a        terminal database; and    -   selecting a Terminal Adapter on the basis of the response.

It is preferred that the request message comprises UnstructuredSupplementary Service Data, and the Unstructured Supplementary ServiceData comprises IP Multimedia Subsystem Centralised Services data.

According to a second aspect of the invention, there is provided amethod of routing a message between a client terminal and a TerminalAdapter, the Terminal Adapter providing an interface between anon-Session Initiation Protocol compliant network and an IMS network,the method comprising:

-   -   sending a message from the client terminal to an IMS Centralised        Services node, said message containing an address of a selected        Terminal Adapter; and    -   sending the message from the IMS Centralised Services node to        the Terminal Adapter at the Terminal Adapter address.

According to a third aspect of the invention, there is provided a methodof routing a message between a client terminal and a Terminal Adapter,the Terminal Adapter providing an interface between a non-SessionInitiation Protocol compliant network and an IMS network, the methodcomprising:

-   -   sending a message from the client terminal to a Mobile services        Switching Centre/Visitor Location Register;    -   sending the message from the Mobile services Switching        Centre/Visitor Location register to an IMS Centralised Services        node at a Home Location Register; and    -   sending the message from the IMS Centralised Services node to        the selected Terminal Adapter.

According to a fourth aspect of the invention, there is provided a nodein a communications network for allocating a Terminal Adapter to aclient terminal, the node comprising:

-   -   means for receiving a request message sent from the client        terminal;    -   means for selecting a Terminal Adapter from a plurality of        Terminal Adapters;    -   means for sending a message to the client terminal, the message        containing the address of the selected Terminal Adapter.

The request message may contain an identifier that identifies the clientterminal; and the means for selecting a Terminal Adapter may use theidentifier to select a Terminal Adapter.

The node may further comprise:

-   -   means for sending a query to a terminal database and/or a        subscriber database;    -   means for receiving a response from the terminal database and/or        a subscriber database;    -   wherein the means for selecting a Terminal Adapter uses the        response to select a Terminal Adapter.

According to a fifth aspect of the invention, there is provided a Mobileservices Switching Centre/Visitor Location Register node for use in amobile communications network, the node comprising:

-   -   means for receiving a message from a client terminal, said        message containing an address of a Terminal Adapter; and    -   means for sending the message to the addressed Terminal Adapter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically an example of a known routing of a USSDmessage;

FIG. 2 illustrates schematically a further example of a known routing ofa USSD message;

FIG. 3 illustrates schematically an access network which uses a TerminalAdapter to access an IMS network;

FIG. 4 illustrates schematically allocation of a Terminal Adapter toUser Equipment in a Circuit Switched Public Land Mobile Network.

FIG. 5 illustrates schematically the routing of a USSD message from UserEquipment to a Terminal Adapter; and

FIG. 6 illustrates schematically an alternative routing of a USSDmessage from User Equipment to a Terminal Adapter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 3, there is illustrated schematically a CircuitSwitched (CS) access network which uses a Terminal Adapter (TA) toaccess an IMS network. User Equipment (UE) acting as an IMS CentralisedServices (ICS) Client in a CS Public Land mobile Network (PLMN)transmits a message via a Mobile services Switching Centre (MSC)/VisitorLocation register (VLR) and then a Home Location Register (HLR) to anICS-Terminal Adapter (TA) in, or at the border of an IMS network. Allcommunications between the UE and the IMS network are via the ICS-TA.

It is desirable to allocate TAs dynamically when they are needed. Toachieve this, a pool of TAs are required, from which TAs are allocatedto subscribers/terminals when signalling takes place. A staticallocation is more expensive compared to a dynamic allocation, as TAsmay have long periods of inactivity and so would not be efficientlyused.

Subscribers may subscribe to different services and access the IMSservices using terminals having a range of capabilities. It is thereforeadvantageous to allocate TAs to subscribers/terminals depending on thetype of terminal and services that need to be supported. Advancedterminals with support for the latest ICS specification would, forexample, require a more advanced TA than simpler terminals. Subscribershaving subscribed to an advanced IMS service portfolio will likewiserequire a more advanced TA. Future services and capabilities may requireadditional TA functionality. As different services and terminals may beused, TAs are grouped together in pools depending on the functionalityrequired of them. A TA is allocated to a subscriber/terminal on thebasis of their requirements.

Referring to FIG. 4, there is illustrated schematically allocation of aTA to a UE in a CS-PLMN. The signalling is as follows:

-   1. An ICS client of the UE sends a request to the network    registering its availability for ICS calls. Unstructured    Supplementary Service Data (USSD) service Code (SC) 22 is used to    indicate this in the example, but it may be any SC value. The    request is forwarded to an ISC-TA Allocator using normal USSD    routing via an MSC/VLR and HLR.-   2. This message is received by a TA-Allocator function. The    TA-Allocator checks the terminal ID and the Terminal Id is used to    determine what type of TA is required. The terminal ID may, for    example, be the International Mobile Equipment Identity (IMEI)    received from the terminal. Alternatively, a Medium Access Control    (MAC) address may be used as a terminal ID, in which case the    terminal will need to retrieve the MAC address prior to sending a    message.-   3. The TA-Allocator may query external databases such as a Terminal    Database or a Subscriber Database such as a Home Subscriber Server    (HSS) to determine what type of TA is required, based on, for    example, the capabilities of the user Equipment or the services    subscribed to by the user. A query towards the HSS may be    Non-Transparent Sh, Transparent Sh or both.-   4. A TA of a certain type is allocated based on the queries in steps    2 and 3. Allocation of a TA may also depend on the load of the    network. The TA-Allocator forwards the HLR-address and/or the    MSC/VLR-address to the allocated TA, to allow the allocated TA to    initiate subsequent network initiated USSD dialogues.-   5. The address of the allocated TA is reported back to the ICS    client in the UE.

Once a TA has been allocated to the UE, any messages sent from the ICSclient in the UE include the address of the TA. USSD routing to the TAshould be performed as efficiently as possible in a CS network with ICSsupport, and should also be available in networks without ICS support.

FIG. 5 shows the optimized routing where the MSC has been upgraded withICS-R (ICS Routing) functionality. ICS-R is a USSD application thatinterprets USSD messages having a specific SC (23 in the example but anySC value may be used). ICS-R takes the TA address in the message thathas been inserted by the UE (this is the TA address returned by theTA-Allocator). The TA-address is used by the ICS-R to route the USSDmessage directly to the TA, without passing the subscriber's HLR. TheICS-R can relay this message either on SS7 or on an IP based protocol,for example Web Service based. In both cases, the MSC address isincluded to allow the TA to start a network initiated action. Bybypassing the HLR, the messaging is sent more efficiently.

The USSD message also contains an ICS activity code and optionally otherparameters. These correspond to an ICS protocol carried inside USSD. AnICS Activity could, for example, be “put call on hold”, “resume call”,“register call forwarding number”, etc.

USSD routing should also be available in legacy networks that do nothave ICS capabilities. Where an MSC/VLR has not been upgraded with ICS-Rfunctionality, normal USSD routing via an HLR is used. When the UE sendsa USSD message to the MSC/VLR, and the MSC/VLR does not recognize theUSSD message (because it does not recognize the SC), the MSC/VLRforwards the message to the subscriber's HLR. The subscriber's HLR hasan ICS-R function, and so is able to interpret the data, and the servicecode in particular, transferred in the USSD message. The HLR reads theTA-address contained in the message and transfers the USSD message tothe TA over SS7 or IP

It will be appreciated by persons skilled in the art that variousmodifications may be made to the embodiments described above withoutdeparting from the scope of the present invention. For example, theabove description relates to accessing an IMS network from a CS network.However, it may apply to accessing an IMS network from any non-SessionInitiation Protocol (SIP) compliant network. Furthermore, whilst thedescription relates to UE, the invention could apply to any clientterminal accessing an IMS network from a non-SIP compliant network.

The invention claimed is:
 1. A method in a node of a communicationnetwork of facilitating access by a client terminal to a service in anInternet Protocol (IP) Multimedia Subsystem (IMS) network from anon-Session Initiation Protocol compliant access network, the methodcomprising: receiving by the node, a request message from the clientterminal, wherein the request message includes a terminal identifierassociated with capabilities of the client terminal, or a servicesubscribed to by a user of the client terminal; in response to receiptof said request message, selecting by the node, a Terminal Adapter froma plurality of Terminal Adapters of different types based on thecapabilities of the client terminal, or based on the services subscribedto by the user of the client terminal, wherein the Terminal Adapterprovides an interface between the non-SIP compliant access network andthe IMS network, and the selected Terminal Adapter is of a typecompatible with the capabilities of the client terminal or the servicessubscribed to by the user of the client terminal; allocating by thenode, the selected Terminal Adapter to the client terminal; and sendingfrom the node to the client terminal, a message reporting an address ofthe allocated Terminal Adapter.
 2. The method according to claim 1,wherein the steps of the method are carried out at a single node.
 3. Themethod according to claim 1, wherein the non-Session Initiation Protocolcompliant access network is a Circuit Switched access network.
 4. Themethod according to claim 1, wherein the terminal identifier is selectedfrom one of an International Mobile Equipment Identity (IMEI) and aMedium Access Control (MAC) address.
 5. The method according to claim 1,wherein said plurality of Terminal Adapters comprises groups of TerminalAdapters, each group compatible with the capabilities of a clientterminal type.
 6. The method according to claim 1, wherein saidplurality of Terminal Adapters comprises groups of Terminal Adapters,each group compatible with the services subscribed to by the user of theclient terminal.
 7. The method according to claim 1, further comprising,prior to allocating the Terminal Adapter, the steps of: sending a queryto a subscriber database or a terminal database; receiving a responsefrom the subscriber database or the terminal database identifying thecapabilities of the client terminal or the services subscribed to by theuser of the terminal; and selecting the Terminal Adapter on the basis ofthe response.
 8. The method according to claim 1, wherein the requestmessage comprises Unstructured Supplementary Service Data, and theUnstructured Supplementary Service Data comprises IP MultimediaSubsystem Centralized Services data.
 9. The method according to claim 1,wherein the step of selecting a Terminal Adapter from a plurality ofTerminal Adapters of different types is also based on a load on thenetwork.
 10. A method of routing a message between a client terminal ina non-Session Initiation Protocol compliant access network and aTerminal Adapter, the Terminal Adapter providing an interface betweenthe non-Session Initiation Protocol compliant access network and an IPMultimedia Subsystem (IMS) network, the method comprising: allocatingthe Terminal Adapter to the client terminal by a Terminal Adapterallocation node, and sending an address of the allocated TerminalAdapter to the client terminal, wherein the Terminal Adapter allocationnode is configured to select the Terminal Adapter from a plurality ofTerminal Adapters of different types based on capabilities of the clientterminal or on services subscribed to by a user of the client terminal,wherein the selected Terminal Adapter is of a type compatible with thecapabilities of the client terminal or the services subscribed to by theuser of the client terminal; receiving by an IMS Centralized Servicesnode, a message from the client terminal containing the address of theallocated Terminal Adapter; and sending the message from the IMSCentralized Services node to the allocated Terminal Adapter at theTerminal Adapter address.
 11. The method according to claim 10, whereinthe IMS Centralized Services node is implemented in a Home LocationRegister, and the step of receiving the message from the client terminalincludes receiving the message in a Mobile services SwitchingCentre/Visitor Location Register, which forwards the message to the IMSCentralized Services node at the Home Location Register.
 12. A node in acommunications network for allocating a Terminal Adapter to a clientterminal operating in a non-SIP compliant access network, the nodecomprising: means for receiving a request message sent from the clientterminal, the request message including a terminal identifier associatedwith capabilities of the client terminal, or a requested serviceidentifier associated with services subscribed to by a user of theclient terminal in an Internet Protocol (IP) Multimedia Subsystem (IMS)network; means for selecting a Terminal Adapter from a plurality ofTerminal Adapters of different types based on the capabilities of theclient terminal, or based on the services subscribed to by the user ofthe client terminal, wherein the Terminal Adapter provides an interfacebetween the non-SIP compliant access network and the IMS network, andthe selected Terminal Adapter is of a type compatible with thecapabilities of the client terminal or the services subscribed to by theuser of the client terminal; and means for sending a message to theclient terminal, the message containing an address of the selectedTerminal Adapter.
 13. The node according to claim 12, furthercomprising: means for sending a query to a terminal database or asubscriber database; and means for receiving a response from theterminal database or the subscriber database identifying thecapabilities of the client terminal or the services subscribed to by theuser of the client terminal; wherein the means for selecting a TerminalAdapter uses the response to select a Terminal Adapter.
 14. A Mobileservices Switching Centre/Visitor Location Register (MSC/VLR) for use ina mobile communications network, the MSC/VLR comprising: means forreceiving a message from a client terminal operating in a non-SIPcompliant access network, said message containing an address of aTerminal Adapter selected from a plurality of Terminal Adapters ofdifferent types and allocated to the client terminal based oncapabilities of the client terminal or on services subscribed to by auser of the client terminal in an Internet Protocol (IP) MultimediaSubsystem (IMS) network; and means for forwarding the message to theaddressed Terminal Adapter.
 15. The method according to claim 10,wherein the IMS Centralized Services node is implemented in a Mobileservices Switching Centre/Visitor Location Register, and the Mobileservices Switching Centre/Visitor Location Register forwards the messagedirectly to the allocated Terminal Adapter at the Terminal Adapteraddress while bypassing a Home Location Register.